Tunable pulsed lasers using dye cells as the gain medium and diffraction gratings as the frequency-selective element have been available since the early 1970s. These early lasers, however, had relatively broad linewidths and poor temporal and spatial beam properties, and produced relatively low powers and/or energies. In addition, these early lasers had relatively many parts and were difficult to align. Relevant publications regarding these early developments are Single mode operation of grazing incidence pulsed dye laser, Opt. Lett. 3. p. 138 (1978) by M. Littman and Narrowband operation of a pulsed dye laser without intracavity beam expansion, J. Appl. Phys., 48,4495 (1977).
It was also discovered that mode-hopping and mode-beating of these tunable pulsed lasers occurred as te laser was tuned over its entire-tuning range. Since output beams that exhibit mode-beating can cause undesirable responses in the materials into which they are introduced, a single longitudinal mode is to be preferred.
It is known that continuous-wave (CW) lasers can operate with very narrow bandwidths. However, to produce pulsed outputs from such lasers, it is necessary to chop the CW output into the desired pulses. The process of chopping the output leads to undesirable inefficiencies and requires complicating circuitry.
Further, it has long been known that gain mediums based on dye cells are very inefficient and relatively short-lived. It has also been known that solid-state gain media are damaged by pump beams whose fluence exceeds a predetermined amount.
It is therefore desirable to have a simple pulsed laser that can produce tunable single-mode outputs over a very broad range of wavelengths at high efficiencies for long periods of time.